Process for making milled toilet soap



Patented Oct. 18, 1938 UNITED STATES PROCESS FOR MIL LED TOILET Victor Mills, Cincinnati, Ohio, assignor to The Procter & Gamble Company, Cincinnati, Ohio,

a corporation of Ohio No Drawing.

Claims.

This invention relates to an improved continuous process for making milled toilet soap.

This application covers that aspect of the in- I vention disclosed in my co-pending application 5 Serial No. 64,525 on a Continuous process for converting saponiflable fats into soap and glycerin, which relates to the employment of the dried material for the manufacture of milled soap.

One object of this invention is to make a milled 1U toilet soap in a continuous operation from fatty material to finished soap with resulting econo- ,mies in operation and space required.

Another object of this invention is to provide 'a milled toilet soap with a controlled percentage of electrolytes.

Another object is to provide an improved method of preparing the partially dried soap for milling.

Another object is to make a milled soap of go unusually smooth texture and freedom from cracks and hard specks. A milled" type soap is made by partially drying, thoroughly kneading, and compressing the soap into an elongated bar which is then cut into individual bars of the desired length and stamped. Such soap is especially desirable for toilet use because when properly made it is mild, smooth in texture, lathers readily, is durable in use, and shows but little tendency to soak up water and 30 become soft during washstand' use. The kneading is accomplished by passing the partially dried soap repeatedly between milling rolls, or through small orifices, to thoroughly break up the grain. The compressing is accomplished by forcing the' slightly warm and plastic soap through an orifice under high pressure in a plodder, a well known device of the soap industry. The size and shape of the plodder orifice depend on the size and shape of the bar desired, and this operation serves to weld the soap into a homogeneous mass. In the manufacture of milled toilet soap it has heretofore been the usual practice to first make a boiled kettle soap in the usual manner by 'saponifying fats or fatty acids with alkali hy- 45 droxide or carbonate, and graining out with salt. Such soaps inevitably contain approximately 30 per cent moisture, about .4 per cent or more of sodium chloride, up to about .1 per cent'of sodium hydroxide, and small quantities of glycerin and 50 possibly some other impurities. These impurities, especially those in the nature of electrolytes, even though small in amount, have. an important influence on the finished product, particularly with reference to ease of milling and development of cracks in the finished product. The

Application April 2, 1936. Serial No. 72,372

kettle soap in molten condition is next crutched to effect uniformity and smoothness, then solidified by cooling in a thin film on cold rolls from ,which it is removed in the form of flakes, which are then passed on long conveying belts through 6' suitable driers where they are exposed to heated drying air to reduce the moisture andvolatile 'matter from about 30 per cent down to a suitable point, usually about 12-16 per cent. Hereinafter I will use 15 'per cent as an example. In this operation some of the flakes are unavoidably overdried, either wholly, or at least on the surface or edges. The flakes from the drier are next milled, or worked, to break up the grain and convert them into a homogeneous plastic mass by passing same repeatedly between heavy rollers,

or by other suitable procedure. Any desired perfume, coloring matter, etc., is incorporated at this stage. The milled product, usually in form of flakes or extruded threads, while still warm and plastic, is then passed through plodders in which the soap is compressed to a uniform homogeneous mass and exudes in the form of a continuous bar of any desired cross section. The continuous bar is cut into suitable lengths and stamped for use.

This operation necessarily requires a large amount of space and consumes a long period of time. It usually takes about ten days in a large soap factory to make a kettle of boiled soap, and 80 several hours additional to crutch, cool and produce and partially dried flakes ready for milling. The remaining operations consisting of milling, plodding and stamping consume but little time.

One of the serious problems in making milled 3Q soap hitherto has been the production of a bar of perfectly smooth texture, free from individual hard specks or any feeling of roughness in use, and free from cracks or tendency to crack. I-Iard specks and rough texture are usually due either to the presence of dirt, which is diflicult to prevent entirely, or to overdried particles of soap resulting from uneven drying of the flakes. No method of drying flakes'with which I am familiar can be depended on to dry all flakes to the same degree.

cut. Cracks may occur in the soap as made, as V evidenced on cutting open the freshly made bar, or they may develop on the surface of the bar after alternate wetting and drying out on the washstand, and in such cases they collect dirt and make the bar unsightly. These cracks are usually due either to lack of plasticity in the soap as plodded, due sometimes 'to too low a temperature, which is a matter within the control of the operator, but more often to the presence of electrolytes in excessive amounts, which is a matter beyond the control of the operator, and which tends to prevent the soap from becomingsufliciently plastic to be welded perfectly into a homogeneous mass.

The solidifying, flaking, and partial drying of the soap preparatory to milling has in the past required expensive equipment, a large amount of space, and considerable expense for operation. Attempts have been made to economize by substituting for these steps the well known spray drying operation wherein thesoap is sprayed into a heated atmosphere, (such as 250-400 F.) to partially dry it preparatory to milling, but such a product does not make a milled soap of smooth texture, apparently for the reason that the surface of the particles has been overdried by exposure to the heated atmosphere and no amount of milling and plodding seems to be able to convert this product into a milled soap bar of smooth texture.

My process oflers a means of overcoming all these difficulties. Hard specks or rough texture can be entirely eliminated because dirt can be easily excluded, as filtered fatty acids and alkali solution may be used, and the entire process is carried out in a closed system, up to the milling stage at least, and there can be no particles that are overdried like those above mentioned because of my novel method of drying. All particles are uniformly heated and are dried by the heat from within the particle itself without exposure to a heated atmosphere outside the particles; hence all particles are subjected to exactly the same drying eflect and are remarkably uniform. Hence, my soap product is of unusually smooth texture and free from hard specks, even -with relatively little milling. The amount of electrolyte is nil or it can be easily regulated at any desired point, thus making possible a product practically free from cracks 'or tendency to crack.

Furthermore, my process has .the advantage of being a continuous process from fatty acids to the 1 v finished bars and oflers a greatsaving in time,

saponifying agent, preferably sodium hydroxide,

in amount to properly saponify the fatty acids; the fatty acids and saponifying agent are continuously proportioned for this purpose by a 7 suitable automatic 'proportioning device. If any builder is to be added, or any electrolyte such as sodium chloride, it may be added to the solution :of the saponifying agent, or it may be added to the [mixer separately in properly and continuously proportioned quantities; usually, however, in making a milled toilet soap, builders are not add-- ed. Very small quantities of electrolyte (usua y NaCl), usually not over 0.5%, in carefully con trolled amounts, are sometimes desirable on account of their effect on the plasticity of the soap. The total amount of water introduced in the mixer is so regulated as to give the desired moisture content in the sprayed comminuted soap product, after allowing for evaporation in the spray chamber. The total amount of water in the soap should not be more than suflicient to form the "neat soap phase, in order to assure ease of handling, but unnecessary water in any, event should be avoided as it must be volatilized later on. No application of heat is necessary in the mixer or subsequently when using fatty acids di-.

rect from the autoclave, as preferred, but if fatty acids derived from any other source are used they are previously heated to a suitable temperature: I prefer for this purpose a temperature in the neighborhood of 470 F. The saponifying agent does not need to be heated more than enough to have it in good pumping condition but it may be heated, if desired, to impart additional heat to the soap before spraying to secure the desired amount of evaporation. It is essential that the temperature of the mixture be high enough to supply the heat required for volatilization of the water in the spraying step without the application of additional heat. The, material in the mixer must necessarily be kept under a sumcient pressure to prevent volatilization of the water at the temperature of mixing, and the mixer should be of sufflcient capacity to keep the materials in contact with each other long enough to insure intimate contact and completion of the chemical reaction. This period need not ordinarily exceed one minute with an eflicient mixer.

zle at a temperature considerably above 212 F.,

usually about 300 to 400 F., and under superatmospheric pressure, the pressure drops suddenly to that of the spray chamber with a consequent drop in temperature and instantaneo'us evaporation of a portion of the water content in the soap. The amount of water evaporated and the temperature of the comminuted soap product will depend on the original temperature and the absolute pressure in the spray chamber, provided of course that there is sufflcient water present. Ifat atmospheric pressure, the temperature of the soap product will .be approximately 212 F., but lower tempera-' tures may readily be obtained by keeping the absolute pressure in the spray chamber at any desired subatmospheric pressure, and using correspondingly more water. The temperature in any case will be substantially that at which water boils. at the pressure of the spray chamber. Thus, with an absolute pressure of 9.6 inches of mercury the temperature will be 160 1". At an absolute pressure of 1.9 inches mercury the temperature will be l00 1". By proper adjustment of the amount of water originally introduced so as to allow for volatilization in the spray chamber, a product of any desired moisture content and ,at any desired temperature may be obtained.

The required initial temperature in the soap to yield a product having the desired moisture content at any desired temperature can be calcuconsisting of irregular shaped particles, not

rounded, mostly of size easily visible to the naked eye, free from glycerin, salt, or other electrolyte, unless intentionally added, and free from any tendency to overdrying on the surface of the particles because they have been dried by heat from within the particles rather than by exposure to heat from outside the particles such as occurs in spraying into a highly heated drying gas in the usual spray drying processes. All the heat for drying my product is stored up within the product under high temperature and pressure conditions before reaching the spray nozzle, and on issuing from the nozzle at a lower pressure there results a bursting or disintegration of the particles due to theinstantaneous volatilization of moisture contained in same. The surface is no drier than the interior, and there are nooverdried particles. The moisture content, the temperature, and the percentage of electrolytes, if any, can easily be controlled at any desired point.

This product therefore when prepared with proper moisture content and temperature so as to have the desired plasticity for milling (about 15 per cent moisture and a temperature about 95 to 100 F.), and free from overdried particles, dirt, or other forms of hard specks, is unusually well adapted'for the subsequent milling and plodding operations, is capable of being milled in the usual apparatus with unusual ease, and is readily compressed to a homogeneous mass free from hard specks or roughness in texture, and free from tendency to crack such as would occur in the presence of electrolytes. In these respects this product is superior to the partially dried flakes as hitherto used for the milling operation.

The partially dried comminuted soap thus obtained is then passed to a soap milling device which may be of any known form. such as milling rolls or a large number of small orifices, and after passing through such devices a sufllcient number of times to thoroughly and uniformly knead the product, it is then compressed into an elongated bar by passing through a plodder of the usual type. At this stage the soap containing the proper amount'of water, usually about 15 per cent, and at a slightly elevated temperature, such as about 105 F., is sufllciently plastic to be compressed into a solid homogeneous mass which issues from the plodder in the form of a continuous elongated bar. This is then out into individual bars of the required length and stamped as desired, by known means.

ExampZef-As an example of my preferred procedure in making a milled toilet soap, I start with a fatty acid mixture consisting of parts tallow fatty acids, 20 parts coconut oil fatty acids and 13.4 parts of dissolved water, at a temperature of about 470 F. as it issues from my continuous autoclaving procedure, and under a pressure sufn'cient to prevent the water from volatilizing (500 pounds per square inch). Any other source of fatty acids could also be used. The fatty acid mixture is fed in a continuous stream to a mixing device while a concut into the desired lengths for use.

tinuous stream of sodium hydroxide solution is likewise fed to the mixing device in properly proportioned amount, which in this caseis 46.4 parts of an aqueous solution of sodium hydrox- Me at 39" Baum at a temperature of 100 F.,

which solution consists of 155 parts of actual sodium hydroxide and 31.0 parts of water. After intimate mixing, this mixture is then sprayed into a chamber having an absolute pressure of 1.9 inches mercury, under which conditions most of the water will volatilize and the temperature of the sprayed product will be reduced to about F. due to the volatilization of waterand the consequent absorption of latent heat. Other data are shown in the table, as follows:

Anhydrous fatty acids lbs Anhydrous sodium hydroxide lbs Water:

Dissolved in fatty acids lbs In NaOH solution lbs Formed in reaction lbs Total in mixture lbs Volatilized lbs Remaining in product lbs Per cent in product 1bs Temperatures:

Fatty acids F NaOH solution F- Mixture as sprayed F Product after spraying F Pressures:

Fatty acids before mixing lbs. per sq. in s Mixr (lbs. per sq. in. minimum) Spray chamber (inches of mercury) Soap product at 15% moisture lbs monly used in the milled soap industry and is passed over and between these rolls several times until it is thoroughly kneaded. Any perfume or coloring matter desired is introduced at the mill. The soap from-the mills in the form of flakes is 'then fed to a plodding device of a type commonly used in the soap industry, in which the flakes are compressed and welded together in a homogeneous mass issuing from the plodder in the form of a continuous bar. This is then A preliminary plodder may be installed between the mill and the regular plodder to convert the flakes to small rods of the nature of spaghetti which assists in maintaining a uniform feed into the main plodder.

Having thus described my invention, what I claim and desire to secure by Letters Patent is: 1. A continuous process for making a soap base and preparing same for the milling step in the manufacture of milled toilet soap which comprises reacting fatty acids at a temperature of approximately 470 F. with an aqueous solution of sodium hydroxide in chemically equivalent quantities .under a pressure sufficient to prevent volatilization of the water, spraying the ture before sprayingbeing so adjusted as to cause volatilization of all water exceeding about 15 per cent in the sprayed product, said product being in solid comminuted form and substantially free from overdried particles containing less than about 15 per cent moisture.

2, In the manufacture of milled soap from a soap base having more moisture and a higher temperature than required for milling, conditioning the soap for milling by reducing the moisture content without forming an overdried skin on the surface of the particles, and reducing the temperature of said soap, comprising first imparting to the soap suificient heat to cause volatilization of all excessmoisture but maintaining a sufiicient pressure during heating to prevent volatilization of moisture before spraying, second, spraying said soap into a chamber in which the absolute pressureis maintained at a point below atmospheric and not greater than 9.6 inches of mercury, the total heat in the soap before spraying and the absolute pressure in the .spray chamber being so adjusted with relation to each other as to cause volatilization of all excess water above approximately fifteen per cent in the sprayed comminuted product by the heat contained within the particles without the application of external heat, whereby the soap iscooled to a solid comminuted form substantially free from overdried particles or underdried particles having a moisture content varying substantially from the aVerage, and then milling said soap while the conditionthus imparted to it remains substantiallyunchanged.

3. In the manufacture of milled soap from a [soap base having more moisture and a higher temperature than required for milling, conditioning the soap for milling by reducing the moisture content without forming an overdried skin,

on the surface of the particles, and reducing the temperature of said soap", comprisingfirst imparting to the soap sumcient heat to cause. volatilization .of all excess moisture but maintaining a sumcient pressure during heating to prevent volatilization of moisture before spraying,-

second, spraying saidisoa p into a chamber in which the absolute pressure is maintained at a point below atmospheric and not greater than 9.6 inches of mercury, the total heat in the soap before spraying and the absolute pressure in the spray chamber being so adjusted with relation to each other as to cause volatilization of all excess water above approximately fifteen per cent in the sprayed comminuted product by the heat contained within the particles, whereby the soap is cooled to a solid comminuted form substantially free from overdried particles or underdried particles having a moisture content varying substantially from the average, and said particles'being substantially free from overdried surw faces having a lower moisture content than the area-see interior of said particles, and then milling said soap while the condition thus imparted to it remains substantially unchanged.

' 4. In the manufacture of milled soapfrom a soap base substantially free from glycerin but having more moisture and a higher temperature than required for milling, conditioning the soap for milling by reducing the moisture content without forming an overdried skin on the surface of the particles, and reducing the temperature of said soap, comprising first imparting to the soap sufllcient heat to cause volatilization of all excess moisture above approximately fifteen per cent but maintaining a suflicient pressure during heating to prevent volatilization of moisture before spraying, second, spraying said soap into a chamber in which the absolute pressure is maintained at a point below atmospheric and not greater than 9.6 inches of mercury, the total heat in the soap before spraying and the absolute pressure in! the spray chamber being so adjusted with relation to each other as to cause volatilization of all excess water above approximately fifteen per cent needed for plasticizing the soap for milling, sa'id volatilization being rcaused by the heat contained within the particles without the application of external heat, whereby the soap is cooled to a solid comminuted form substantially free from overdried particles or underdried particles having a moisture content varying substantially from the average, and then milling said soap while the condition thus imparted to its remains substantially unchanged.

5. In the manufacture of milled soap from a soap base substantially 'free from glycerin but containing excessive moisture for millinglpurposes and having a temperature in excess of 212 F. and a superatmospheric pressure sufllcient to prevent volatilization of said moisture, conditioning the soap for milling by reducing the moisture content without forming an overdried skin on the surface of the particles and reducing the temperature of said soap, comprising spraying said soap into a chamber having an absolute pressure of about 1.9 inches of mercury, the total heat and the total moisturerin the soap before spraying being so adjusted with relation to each other as to causevolatilization of all water ex- 

